This is the definition of multitrack recording. Weather you use multiple soundcards or you use one soundcard with multiple inputs is irrelevant to that. Multitrack recording allows you to record different inputs, but they are all part of a song. The big advantage of this is that you can always delete something and then record it again. Also you can edit the tracks one by one.

I thought when you said multitrack recording you meant the older method eg you would record one instrument at a time and then record more.

Maybe I should have explained myself earlier yes. But there are multiple ways of multitrack recording. You can also do multitrack recording with a single soundcard and a single input, as long as you make each recording on a different track. But in this case I meant for example putting the Guitar on track 1, putting the vocals on track 2 and 3, and other instruments on 4, 5, 6 etc, etc, but you record them all at the same time.